How do you find co-founders (and figure out if they’re a good fit)?

The more visible I become on platforms, the more opportunities I receive (not just sponsored ones).

Quite often, people reach out saying they’re looking for a marketing co-founder.

And practically every month, there’s someone with “another revolutionary idea,” “the next big thing,” “a multimillion or multibillion-dollar business”… but then you never hear about them again.

Maybe something is wrong with me, but so far no one has been able to convince me (maybe because I’m very selective). But also maybe because:

1. their idea doesn’t really grab me (or it’s outside my field and interests)

2. they don’t have any past track record or success rate

3. they don’t present any strategic plan or explain how they’ll execute the vision

If you were getting similar requests, what criteria would you use to decide whether to join?
Maybe a better question is: What do you look for in founders and their idea before becoming a co-founder?